1. Field of the Invention
The present invention relates to a data transmission apparatus and data transmission method, more particularly to a data transmission apparatus and data transmission method in for example a cable television company broadcasting over multiple channels and equipped with a recording and/or reproducing system which stores all of the audio and/or video data of programs and commercials to be broadcast over the different channels all together and reproduces the audio and/or video data of the individual programs or commercials for transmission over individual channels.
2. Description of the Related Art
In recent years, cable TV (CATV) companies etc. have been upgrading their systems so offer a greater number of channels. Along with this, there is a growing demand for systems which, unlike the video tape recorders of the related art, enable simultaneous recording or reproduction of audio and/or video data of several programs or commercials to or from a single audio and/or video data recording and reproducing apparatus and, further, simultaneous recording and reproduction. In response to this demand, apparatuses called xe2x80x9cvideo serversxe2x80x9d (or called xe2x80x9cAV (audio and/or video) serversxe2x80x9d) using hard disks and other randomly accessible recording media are being increasingly used for recording and reproducing the audio and/or video data.
In general, a video server in a cable television company must be able to transfer data at a fast rate due to the demands on image quality and sound quality and must have a large storage capacity in order to be able to record long hours of data. Effort has been made to speed up the rate of transfer of data and increase the storage capacity by using data recording and reproducing apparatuses equipped with a bank of hard disk drives for parallel storage and processing of audio and/or video data. In addition, effort has been made to ensure reliable service even if one or more of the hard disk drives malfunctions by the recording of parity data. These efforts have enabled the realization of a multi-channel video server which can simultaneously transmit audio and/or video data of several programs or commercials, recorded in a dispersed manner, over multiple channels or can transmit the same data over multiple channels shifted in timing of reproduction even when the number of channels required for transmission differ due to the content or format of the program or commercial to be broadcast and therefore can offer a variety of services, for example, xe2x80x9cvideo on demandxe2x80x9d (VOD) and xe2x80x9cnear video on demandxe2x80x9d (NVOD).
There are, however, many types of cable television companies etc.xe2x80x94from small-sized operations broadcasting over only one to three channels to largesized operations broadcasting over dozens or even hundreds of channels. The functions and performances required for the server system differ in different cable television companies etc.. Therefore, in the past, it had been necessary to individually design server systems in accordance with the scale of operations of the companies etc. The expenses required for designing the systems therefore increased the price of server systems.
Further, such individually designed server systems are difficult to modify, for example, when the cable television company expands its operations and wants to increase the number of channels offered. It is therefore not possible to flexibly increase the number of channels.
Of course, it is possible to simply use the identical configuration server system in different sizes of cable television companies etc., but to do this would require the adoption of a configuration suited to the large sized operation companies etc.. This would end up forcing small sized operations to install unnecessarily large sized, expensive server systems.
An object of the present invention is to provide data transmission apparatus and data transmission method enabling realization of a data recording and/or reproducing system enabling configuration of a server system tailored to the scale of operations of the cable television company etc. by assembling unit modules of identical configurations.
Another object of the present invention is to provide a data transmission apparatus and data transmission method enabling realization of a data recording and/or reproducing system enabling flexible changes in the specifications of a server system to deal with increases in the number of channels offered by the cable television company etc.
According to a first aspect of the present invention, there is provided a data transmission apparatus having unit modules connected in cascade in a plurality (x; 2xe2x89xa6x) of stages and a list converting means, wherein each of the unit modules has a recording and/or reproducing means, a first-list generating means for generating a first list indicating the data to be recorded in the recording and/or reproducing means, a second-list receiving means for receiving a second list indicating the data to be reproduced from the recording and/or reproducing means, and a data supplying means for supplying the reproduced data to the next stage unit module; the recording and/or reproducing means of each of the unit modules records the data indicated in the first list generated by the first-list generating means among the data supplied from the outside and reproduces the data indicated in the second list received at the second-list receiving means; and the list converting means converts a first list generated by a first-list generating means of a y(2xe2x89xa6yxe2x89xa6x)th stage unit module to a second list and outputs the same to the second-list receiving means of all unit modules or some unit modules of the (yxe2x88x921)th stage.
Preferably, the first list and the second list contain at least status data indicating whether the data indicated by the first list and the second list have been recorded in the recording and/or reproducing means or have not been recorded; and the recording and/or reproducing means of each of the unit modules reproduces the data which the corresponding status data indicates have not been recorded among the data indicated in the received second list.
Alternatively, preferably, the first list and the second list contain at least status data indicating whether the data indicated by the first list and the second list have been recorded in the recording and/or reproducing means or have not been recorded; the first-list generating means of a unit module supplies a third list comprised of the status data indicating data have not been recorded out of the first list to the list converting means; and the list converting means converts the status data of the third list generated by a first-list generating means of a y-th stage unit module to a second list.
Preferably, the data is video data and/or audio data.
According to a second aspect of the present invention, there is provided a data transmission method for transmitting data from unit modules, each including recording and/or reproducing means for recording data supplied from the outside and reproducing the recorded. data, connected in cascade in a plurality of stages (x; 2xe2x89xa6x), comprising a first step of generating a first list indicating data to be recorded in a recording and/or reproducing means of a y(2xe2x89xa6yxe2x89xa6x)th stage unit module; a second step of converting the first list generated at the first step to a second list indicating the data recorded in the recording and/or reproducing means to be reproduced; a third step of outputting the second list converted at the second step to all of the unit modules or some of the unit modules of the (yxe2x88x921)th stage; and a fourth step of receiving the second list output at the third step and reproducing the recorded data from the recording and/or reproducing means based on the second list.
Preferably, there is the further step of the y-th stage unit module generating the second list and reproducing the data recorded in the recording and/or reproducing means of the y-th stage unit module.
Preferably, there is the further step of a unit module of the (yxe2x88x921)th stage receiving the second list output at the third step, converting the same to the first list, and recording the data indicated in the first list among the data supplied from the outside in the recording and/or reproducing means of the (yxe2x88x921)th stage.